The present invention relates to an item transport, and more particularly to a system for detecting both jammed articles and failures of sensors within the detector itself.
The assignee of the present invention has long been involved in providing mailing machines and systems for government and industry, which efficiently and expeditiously handle all types of mailing needs. One of the areas of mail handling which has yet to be extensively explored, is the automatic handling of both sealed and unsealed inter mixed mail without the need for operator intervention.
Machines have been developed which automatically weigh mixed mail, whether sealed or unsealed, and imprint the correct postage thereon. One such machine is illustrated in U.S. Pat. No. 3,890,492; issued June 17, 1975, and assigned to the assignee of the present invention. That machine is designed to weigh and print proper postage on 7,000 units of mail per hour without operator intervention. An operator's role is normally limited to placing unmetered mail on a feeder deck at one end of the machine, setting the proper postal rate for the class of mail being handled, starting the machine, and removing the metered mail from a stacker at the other end of the machine.
Since such a machine has an extremely high throughput and is expected to handle items which may be bent or distorted during preparation or before reaching the machine, it is not inconceivable that items may become jammed within the machine. While an operator might hover over the machine to watch for jamming, this would defeat one of the reasons for automating the machine in the first place. Moreover, since the throughput of such a machine is better than one document per second, and since jams should occur infrequently, if ever, an operator whose attention has wandered would not react quickly enough to prevent a serious jam, with the possible consequences of mutilated mail and/or damage to the machine.
Time-based detecting systems are known. In such systems, pieces of mail are expected to pass certain points within the machine at predetermined times. Failure of a piece of mail to arrive at the point by the predetermined time is interpreted as a jam condition.
However, since mail is driven through such machines by friction rollers, a roller may slip for a moment, causing a hesitation in the feeding of mail. This hesitation, although not affecting the primary functions of the mail handling machine, may prevent a piece of mail from reaching a predetermined point when it is supposed to. If that occurs, an invalid jam signal will be generated. Consequently, the machine may be stopped notwithstanding it is processing mail in a normal manner.